U.S. Pat. No. 6,121,168, hereby incorporated by reference herein, describes a diatomaceous earth in the form of porous, cylindrical particles as friction modifier in wet paper friction material. U.S. Pat. No. 6,586,373 discloses a wet friction material including filler including disc-shaped diatomaceous earth and another filler material having a high Mohs hardness, from 8 to 9.5, such as silicon nitride, alumina, aluminum silicate and others. U.S. Patent Publication No. 2014/0087982 discloses microcapsules of lubricant additives in an oil.